An internal combustion engine uses a cylinder device moved by an explosive power generated by the combustion of a fuel. A gasoline engine or a diesel engine operates the cylinder device by an explosive power by spraying a fuel together with air for combustion into the cylinder device and then by igniting and exploding the fuel.
As shown in FIG. 1, the cylinder device includes a cylinder block 10 and a piston 20 that moves in a straight-line reciprocating motion within the cylinder block 10, and a cylinder liner 11 having excellent wear resistance may be inserted into the cylinder block 10 when necessary.
Accordingly, when the cylinder liner 11 is not additionally inserted, an inner surface of the cylinder block 10 serves as a cylinder bore side BS, and when the cylinder liner 11 is additionally inserted, an inner surface of the cylinder liner 11 serves as a cylinder bore side BS′.
Further, a piston ring R is fitted to a top of the piston 20 moving along the inside of the cylinder block 10, and a bottom of the piston 20 is provided with a piston skirt 20a. Further, the piston 20 is connected to a connecting rod 22 through a piston pin 21, the connecting rod 22 is connected to a crankshaft 23, and a CRS rotational shaft is fitted to the crankshaft 23.
Meanwhile, in the above-described cylinder device, when a contact surface pressure between the piston 20 and the cylinder bore side BS or BS′ which cause a relative motion is high and a sliding speed when moving in the relative motion is slow, two contact surfaces enter a mixed lubrication state in which solid contact or a boundary lubrication state is mixed.
In the mixed lubrication state, the solid contact leads to a rapid rise in temperature in fine areas of two surfaces, and the temperature rise causes plastic deformation and fatigue failure on the two surfaces. For this reason, wear particles broken from any one surface of the two surfaces further increase friction and wear on the contact surfaces.
Accordingly, in order to enhance lubrication performance on the two contact surfaces moving in the relative motion in the mixed lubrication state, a method of processing fine textures on the cylinder bore side BS or BS′ has recently been attempted.
As the method of processing the fine textures, there are a method using a laser (Laser Surface Texturing; LST), a machining method using a machine tool, an ion beam processing method using electrical or physical energy of ions dissociated from gases in a vacuum state, and a processing method using a semiconductor etching process.
As mentioned above, when the fine textures are formed on the cylinder bore side BS or BS′ through the above-stated processing methods, since it is already known that the fine textures cause a fluid dynamic-pressure effect, store a lubricant, and collect the wear particles, the fine textures formed on the cylinder bore side have been studied in various fields.
Unfortunately, in order to minimize friction and wear by processing the fine textures, it is very important to determine the shape and arrangement of the textures so as to be appropriate for operating conditions of machine elements.
That is, since the shape and arrangement of the fine textures capable of minimizing friction and wear are largely affected by physical restraint conditions and operating conditions such as a contact type, an applied load, and a sliding speed of two objects that move in a relative motion, there is much difficulty in finding an optimum point at which friction and wear are minimized. Particularly, a sliding motion is caused between the cylinder liner 11 for an engine and the piston 20, and conditions of the sliding motion continue to change.
Furthermore, since the piston 20 connected to the crankshaft 23 through the connecting rod 22 moves in a straight-line reciprocating motion in an axial direction of the cylinder bore side BS or BS′, a sliding speed becomes zero (0) at top dead center TDC and bottom dead center BDC, whereas the sliding speed continues to change on the contact surfaces of the cylinder bore side BS or BS′ and the piston 20.
Moreover, since the sliding speed becomes zero (0) at the top dead center TDC and bottom dead center BDC, the two contact surfaces enter the mixed lubrication state in which solid contact or a boundary lubrication state is mixed. Particularly, since a high-temperature operating environment is set up near the top dead center TDC due to an explosion stroke, viscosity of the lubricant is low. Thus, the cylinder liner 11 and the piston ring R is under a poorer wear and friction environment.
Accordingly, as the engine operating environment becomes worse so as to be prone to wear the piston ring R, a method capable of further reducing the wear of the piston ring R than the typical method is needed.
In addition, the piston 20 of the internal combustion engine moves in a pivoting motion around the piston pin 21 while reciprocating at a stroke distance S due to a combustion pressure or a frictional force generated between the piston ring R and the cylinder bore side BS or BS′, and the pivoting motion is called a piston secondary motion.
Accordingly, since the cylinder bore side BS or BS′ comes in direct contact with the piston 20 as well as the piston ring R due to the pivoting motion of the secondary motion, there is a problem in that the amount of wear of the cylinder bore side BS or BS′ is further increased due to the direct contact caused by the pivoting motion of the piston 20.
Meanwhile, in order to reduce the wear of the cylinder bore side BS or BS′, a method such as heat treatment, surface roughness improvement or honing has been conventionally used. However, in recent years, as the engine operating environment becomes worse so as to be prone to wear the piston ring R and the cylinder bore side BS or BS′, there is a need for a method capable of further effectively reducing the wear of the cylinder bore side BS or BS′ and the piston ring R that the typical method.
For this reason, Korean Patent Laid-Open Publication No. 2011-26739 suggests a processing method capable of enhancing lubrication performance while reducing manufacturing cost and processing time by processing the fine textures on the cylinder bore side BS or BS′ so as to further reduce the wear of the piston ring R and the cylinder bore side BS or BS′ than the method such as heat treatment, surface roughness improvement or honing.
Disadvantageously, since the method of processing the fine textures does not solve the wear caused by a great change in an instantaneous speed at the top dead center TDC and the bottom dead center BDC when the piston 20 reciprocates and does not also solve the wear caused by the pivoting motion of the piston secondary motion, the method of processing the fine textures does not provide an optimum effect.
In addition, engine oil consumption is one of serious problems caused between the cylinder bore side BS or BS′ and the piston. The engine oil consumption is mostly caused between the cylinder bore side BS or BS′ and the piston 20, and major causes thereof are as follows.
That is, engine oil stays between fine honing grooves on the cylinder bore side BS or BS′, and the oil vaporizes at a high-temperature condition or is introduced into a combustion chamber through the piston ring R in a rising stroke of the piston. Since the introduced engine oil is combusted during the combustion, the engine oil is consumed.
In order to reduce the engine oil consumption, the deformation of a cylinder bore may be minimized or the shape and tension of the piston ring R may be adjusted. However, since the deformation of the cylinder bore is mostly caused when a cylinder head (not shown) is fastened to an upper end of the cylinder block 10 at which the cylinder bore is positioned, it is required to reduce the engine oil consumption by slightly reducing the matching of the piston ring R with the cylinder bore side BS or BS′.
That is, the piston ring R include a top ring, a second ring, and an oil ring. At this time, it is require to reduce the engine oil consumption while preventing a deterioration in the lubrication performance by optimizing conditions of the rings. For this reason, a method of minimizing tension of the piston ring R is recently used to enhance engine fuel efficiency, but when the tension of the piston ring R is too reduced, there is a problem in that the engine oil consumption is further increased.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.